The present invention relates to a looper which rotates in a horizontal plane, preferably for a double lock-stitch sewing machine.
More particularly, the invention relates to a bobbin case for such a looper, having improved elements for guiding the thread contained therein.
Such a looper typically has a bobbin case, which is secured against rotation, with a looper-thread bobbin within it An adjustable leaf spring is provided on its circumference, and the bobbin case wall. has an opening for the emergence of a looper thread. Such a looper may be equipped with a thread-cutting device. The thread-cutting device may include a thread catcher which is swingable in a horizontal plane which lies below the plane of the top of the bobbin case.
A looper which has the foregoing features is known from German Patent No. 19 41 681 and U.S Pat. No. 3,658,021. The known looper has a bobbin case which is secured against rotation and consists of two parts, comprising an upper bobbin-case part and a lower bobbin-case part The lower bobbin-case part, which is mounted in the lopper, receives the upper part in form-locked manner by suitable shaping, the looper-thread bobbin being placed between said parts. By means of a swingable retaining clip which is mounted in a spindle sleeve provided in the lower part of the bobbin case, the assembled upper and lower bobbin-case parts can be locked in position. A protruding circumferential surface on the upper part of the bobbin case receives on its periphery an adjustable leaf spring for applying a defined thread tensioning force to the looper thread. Furthermore, an opening for the emergence of the looper thread is provided in the wall surface, under the spring arm of the leaf spring.
A known thread cutting device for such a double lock-stitch sewing machine has, inter alia, a thread catcher which is swingable in a horizontal plane, which lies below the plane of the top of the bobbin case. In this way, it is made possible to cut both the part of the needle-thread loop which leads to the material being sewn, and the looper thread, closely below the material being sewn.
However, a significant disadvantage of the known looper is that the bobbin case consists of two parts. Due to this two-part construction, the time required for changing bobbins (replacement of an empty looper-thread bobbin by a full one), as well as for threading the looper-thread, is frequently considered unreasonably long Furthermore, a bobbin case which consists of two parts results in greater manufacturing and stocking expenses than a bobbin case consisting of a single part.